The present invention relates to piston rings for internal combustion engines and, more particularly, to an oil control ring to minimize the oil consumption of piston engines.
The difference in diameter between a piston and the cylinder in which it operates necessitates the use of some type of a sealing arrangement. The sealing arrangement is necessary if any substantial amount of compression is to be developed, and if excessive movement of oil from the crankcase into the combustion chamber is to be prevented. It is conventional practice to provide one or more peripheral grooves on the piston, and to install resilient rings in these grooves which are the approximate form of an interrupted circle. It is the intention that the ring or rings should bear directly against the cylinder wall, and should affect a seal against the sides of the groove in which the ring is positioned.
The inevitable difference between the width of the ring groove and the thickness of the ring creates a problem which has proven to be extremely difficult to solve. At least a few thousandths of an inch clearance is required between the ring and the groove in order to permit the ring to move and to position itself radially under its own resiliency. As the combined effect of inertia and/or gas pressure urges a ring against one particular wall of the groove, it is obvious that the gas pressure or oil can find its way in the clearance area between the ring and the opposite side of the groove. The periodic nature of both the inertia and the gas pressure forces is such that conventional ring installations exhibit a tendency to move back and forth in a periodic relationship in the groove. This movement causes a corresponding series of periods in which the ring permits the passage of oil or gas pressure around it. It is generally recognized that oil will tend to move around underneath and in back of a ring, and gradually work its way into the upper area of the cylinder where it is carbonized by the combustion heat.
It is recognized, of course, that the oil ring should permit enough lubricant to remain on the cylinder wall to sufficiently lubricate the one or more compression rings. The essential function of an oil ring, then, is not to scrape all of the oil from the cylinder wall, but to meter lubricant to the compression rings by permitting a thin, uniform, consistent film of oil to be retained along the cylinder wall. Theoretically, it is easier to provide this consistency with a single rail oil ring design, rather than a double rail oil ring design, since it is much more difficult to manufacture a double rail wherein both rails provide consistent pressure against the cylinder wall.
It is seen then that there exists a need for an oil control ring that provides a consistent amount of oil to the cylinders to properly lubricate the compression rings, without allowing excess oil which could impair engine performance or contaminate engine exhaust.